The present invention relates to a polytetrafluoroethylene (PTFE) tape made of at least two layers of polytetrafluoroethylene of different colors, suitable for marking with a laser.
It will be understood that marking with a laser consists in producing writing on the tape by irradiating the tape with the aid of a laser beam, especially a CO.sub.2 laser. By appropriately controlling the intensity of the laser beam, perforations are produced in the upper layer of the tape, leaving the color of the underlying layer appearing in the perforated regions, thus forming the desired marking.
Multilayer PTFE tapes suitable for marking with a laser and employed chiefly for sheathing electrical cables are known.
In this case the tape provides an insulation function like traditional PTFE tapes and is capable of receiving written cable identification by marking with a laser.
Known tapes which are suitable for marking with a laser usually comprise a plurality of the very thin layers of cured PTFE between which layers of another fluorinated resin, such as FEP and/or PFA, are arranged, the tape itself being coated with FEP and/or PFA.
The presence of these other fluorinated resins is necessary to permit a satisfactory adhesion of the tape layers to each other and of the tape to the support onto which it is wound, especially an electrical cable.
The manufacture of such a tape comprising a large number of layers requires the use of a complex and costly wet-route process consisting in depositing successive layers of fluorinated resins as a dispersion, the process involving stages of drying and of curing at temperatures above the gelling temperature of PTFE.
The product obtained is therefore particularly costly.
In addition, during the marking with a laser beam, bubbles and blisters are found to form in the tape, which are due to a retention, within the layers of the tape, of the gaseous products of the reaction induced by the irradiation.